Unless specifically defined, the terms “Radio-opaque” or “Radiopaque” have same meaning. Stents, artificial grafts, and related endoluminal devices are currently used by medical practitioners to treat tubular body vessels or ducts that become so narrowed (stenosed) that flow of blood or other biological fluids is restricted. Such narrowing (stenosis) occurs, for example, as a result of the disease process known as arteriosclerosis. While stents are most often used to “prop open” blood vessels, they can also be used to reinforce collapsed or narrowed tubular structures in the respiratory system, the reproductive system, bile or liver ducts or any other tubular body structure.
Vascular grafts made of polytetrafluoroethylene (PTFE) are typically used to replace or repair damaged or occluded blood vessels within the body. However, they may require additional means for anchoring the graft within the blood vessel, such as sutures, clamps, or similarly functioning elements to overcome retraction. Stents have been used in combination with grafts to provide endovascular prostheses which are capable of maintaining their fit against blood vessel walls. The use of grafts along with stents also serves to overcome a problem found with stents where smooth muscle cells and other tissues can grow through the stent's mesh-like openings, resulting in restenosis of the vessel.
PTFE has proven unusually advantageous as a material from which to fabricate blood vessel grafts or prostheses, because PTFE is extremely biocompatible, causing little or no immunogenic reaction when placed within the human body. In its preferred form, expanded PTFE (ePTFE), the material is light, porous and readily colonized by living cells so that it becomes a permanent part of the body. The process of making ePTFE of vascular graft grade is well known to one of ordinary skill in the art. Suffice it to say that the critical step in this process is the expansion of PTFE into ePTFE. This expansion represents a controlled longitudinal stretching in which the PTFE is stretched to several hundred percent of its original length. Examples of ePTFE grafts are shown and described in U.S. Pat. Nos. 5,641,443; 5,827,327; 5,861,026; 5,641,443; 5,827,327; 6,203,735; 6,221,101; 6,436,135; and 6,589,278, each of which is incorporated in its entirety by reference. Grafts made from materials other than ePTFE that have been utilized include, for example, Dacron mesh reinforced umbilical tissues, bovine collagen, polyester knitted collagen, tricot knitted polyester collagen impregnated, and polyurethane (available under the trademark Vectra®).
Stent grafts are a prosthetic device designed to maintain the patency of various vessels in the body, including the tracheobronchial tree. The device may include a balloon expandable stent encapsulated with ePTFE or alternatively a self-expanding Nitinol stent encapsulated with ePTFE and pre-loaded on a flexible delivery system. One example of the latter is known commercially as “Fluency®,” which is marketed by C.R. Bard Peripheral Vascular Inc. Examples of such stent-graft is shown and described in U.S. Pat. Nos. 6,053,941; 6,124,523; 6,383,214; 6,451,047; and 6,797,217, each of which is incorporated in its entirety by reference. The field of covering stents with polymeric coatings and ePTFE in particular has been substantially explored by those skilled in the art. One popular way of covering the stent with ePTFE material is to encapsulate it within two layers of ePTFE which are subsequently fused together by heat in places where the two layers are in contact through openings in the stent wall. This provides a solid one-piece device that can be expanded and contracted without an ePTFE layer delaminating.
Implantation of a graft or an encapsulated stent into the vasculature of a patient involves very precise techniques. Generally, the device is guided to the diseased or damaged portion of a blood vessel via an implantation apparatus that deploys the graft or the encapsulated stent at the desired location. In order to pinpoint the location during deployment, the medical specialist will generally utilize a fluoroscope to observe the deployment by means of X rays. Deployment of an encapsulated stent at an unintended location can result in immediate trauma, as well as increasing the invasiveness associated with multiple deployment attempts and/or relocation of a deployed device. In addition, visualization of the implanted device is essential for implantation, follow-up inspection and treatment. Accordingly, in order to implant the encapsulated stent using fluoroscopy, some portion of the stent, graft or implantation device should be radiopaque.
Stents that are implanted and expanded within a blood vessel using a balloon catheter can be located by fluoroscopy because the balloon catheter can have radiopaque features incorporated therein that may be used as a visual marker. However, if the balloon moves after expansion of the stent, correct placement of the stent, in the absence of a radiopaque marker incorporated into the stent, cannot be confirmed. A self-expanding stent can be generally delivered to the damaged or diseased site via a constraining member in the form of a catheter or sheath and can be deployed by removing the constraining member. In order to direct the delivery device and the self-expanding stent to the precise location for deployment, the radiopacity must be incorporated into the device or the constraining member to confirm the correct placement within the vessel.
In addition to visually verifying the location of the implanted stent or graft, it may be necessary to visually verify the orientation of the graft or stent, and/or visually determine if the implant has been twisted or kinked. A properly configured radiopaque marker can facilitate meeting these visual needs. Moreover, radiopaque markers incorporated into the material of a graft or encapsulated stent can provide an alternative to exposed “spoon” type markers that can contact areas of the blood vessel being treated.